Vitamin D and calcium metabolism

Abnormal Bone Metabolism May Be a Primary Causative Factor of Keel Bone Fractures in Laying Hens

Simple Summary

Keel is an essential structural bone, providing anchorage for the attachment of large breast muscles in birds, allowing them to flap wings and provide proper ventilation for their lungs during flight. Previous studies reported that keel bone damage (especially fractures) negatively affects the welfare, health, production performance, eggshell quality, and mobility of laying hens contained in different housing systems. Furthermore, various factors affect keel bone damage, including nutrition, age, housing systems, and strains of laying hens. However, studies on the effects of abnormal bone metabolism and development on keel bone damage in laying hens are limited. Therefore, this study aimed to investigate the impacts of bone metabolism and development status on keel bone damage by determining the levels of serum bone turnover markers in laying hens. The results showed that laying hens with impaired keel bone had significantly altered levels of serum Ca and P metabolism-related and osteoblast and osteoclast activity-related markers compared to those in laying hens with normal keel bone. Thus, these results indicated that abnormal bone metabolism before keel bone damage reflected by varying levels of serum bone turnover markers might be a pivotal factor causing keel bone damage in laying hens. Our results also provide new insights into the occurrence of keel bone damage in laying hens.

Abstract

Keel bone damage negatively affects the welfare, production performance, egg quality, and mobility of laying hens. This study aimed to investigate whether abnormal bone metabolism causes keel bone damage in laying hens. Eighty Hy-line Brown laying hens were housed in eight furnished cages with 10 birds per cage and studied from 18 to 29 weeks of age (WOA). Accordingly, keel bone status was assessed at 18, 22, 25, and 29 WOA using the X-ray method, and the serum samples of laying hens with normal keel (NK), deviated keel (DK), and fractured keel (FK) that occurred at 29 WOA were collected across all the time-points. Subsequently, the serum samples were used to measure markers related to the metabolism of Ca and P and activities of osteoblast and osteoclast. The results showed that FK laying hens had lighter bodyweight than NK and DK birds throughout the trial (p < 0.05), while the keel bone length and weight were not different in NK, DK, and FK hens at 29 WOA (p > 0.05). Moreover, bone hematoxylin and eosin (H&E) staining and tartrate-resistant acid phosphatase (TRAP) staining indicated that damaged keel bone had evident pathological changes. In the FK hens, serum P level was reduced but serum 1,25-dihydroxy-vitamin D₃ (1,25-(OH)₂D₃) and 25-hydroxyvitamin D₃ (25-OHD₃) levels were elevated compared to NK hens (p < 0.05). Additionally, DK hens had higher levels of serum 1,25-(OH)₂D₃, parathyroid hormone (PTH) and calcitonin (CT), and lower level of serum 25-OHD₃ than the NK birds (p < 0.05). Furthermore, serum alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG), TRAP, and corticosterone (CORT) levels were elevated in DK and FK hens compared to NK hens (p < 0.05). The levels of serum Ca, P, PTH, ALP, TRAP, OPG, OC, and CORT in laying hens fluctuated with the age of the birds. Generally, the results of this study indicate that keel bone damage, especially fractures, could be associated with abnormal bone metabolism in laying hens.

Antiproliferative activity of side-chain truncated vitamin D analogs (PRI-1203 and PRI-1204) against human malignant melanoma cell lines

Vitamin D compounds are versatile molecules widely considered as promising agents in cancer prevention and treatment, including melanoma. Previously we investigated series of double point modified vitamin D₂ analogs as well as non-calcemic 20S-hydroxyvitamin D₃ and 21-hydroxypregnacalciferol as to their anti-melanoma activity. Surprisingly, short side-chain vitamin D analogs were found to be biologically active compounds. Thus, here we tested novel derivatives of pregnacalciferol with an additional hydroxyl at the end of the truncated side chain, PRI-1203 and PRI-1204, as to their potency against human melanoma A375 and RPMI7951 cell lines. Tested compounds are geometric isomers, with 19-methylene positioned in PRI-1203 like in a calcitriol molecule, but reversed in the PRI-1204 analog to the (5E,7E) geometry (5,6-trans). We noticed a decrease in cells viability exerted by PRI-1203. The antiproliferative effect of PRI-1204 was very low, emphasizing the importance of the natural 19-methylene geometry in the PRI-1203. PRI-1203 was also effective in inhibition of A375 melanoma cells migration. PRI-1203, but not PRI-1204, increased the percentage of A375 and RPMI7951 melanoma cells in the G0/G1 phase of cell cycle, possibly in a p21 and p27 independent manner. Both, analogs have very low effect on the level of CYP24A1 mRNA, in comparison to active form of vitamin D - 1.25(OH)2D3. In addition, both tested compounds failed to elicit VDR translocation to the nucleus. Thus, it could be postulated that side chain shortening strongly affects binding of analogs to VDR and activation of genomic responses, however do not impair their antiproliferative activities.

Effect of dietary xylooligosaccharides on intestinal characteristics, gut microbiota, cecal short-chain fatty acids, and plasma immune parameters of laying hens

This study examined the prebiotic effects of xylooligosaccharides (XOS) on intestinal characteristics, gut microbiota, cecal short-chain fatty acids, plasma calcium metabolism, and immune parameters of laying hens. A total of 1,080 White Lohmann laying hens (28 wk of age) was assigned to 6 dietary treatments that included XOS at concentrations of 0, 0.01, 0.02, 0.03, 0.04, or 0.05% for 8 weeks. Each treatment had 6 replicates with 10 cages (3 birds/cage). Blood, intestinal tissues, and cecal digesta samples were collected from chickens at the end of the experiment. Villus height, crypt depth, the villus to crypt (VH: CD) ratio, and the relative length of different intestinal sections were evaluated. Additionally, the number of microorganisms and the content of short-chain fatty acids in cecal digesta samples were determined. Plasma concentrations of immunoglobulin A (IgA), immunoglobulin G, immunoglobulin M (IgM), interleukin 2 (IL-2), tumor necrosis factor-α(TNF-α), 1, 25-dihydroxyvitamin D3 (1,25(OH)2D3), calcitonin (CT), and parathyroid hormone (PTH) were also determined. The results showed that villus height and the VH: CD ratio of the jejunum were increased (linear, P < 0.01) with the increase in dietary XOS concentration, and the relative length of the jejunum (P = 0.03) was increased significantly in XOS diets. Dietary supplementation of XOS significantly increased (linear, P < 0.01) the number of Bifidobacteria in the cecum; however, total bacteria count, Lactobacillus, and Escherichia coli in the cecum were not affected by XOS supplementation. In addition, inclusion of XOS increased (linear, P < 0.01) the content of butyrate in the cecum; and the content of acetic acid showed a linear increasing trend (P = 0.053) with increasing concentration of XOS in the diets. Supplementation with XOS increased (quadratic, P < 0.05) the content of 1,25(OH)2D3 in plasma. There were no significant differences (P > 0.05) in the content of CT and PTH among dietary treatments. Furthermore, dietary XOS increased contents of IgA (linear, P < 0.05), TNF-α (linear, P < 0.05), IgM (linear, P < 0.05; quadratic, P < 0.05), and IL-2 (quadratic, P < 0.05). Taken together, it was suggested that supplemental XOS can enhance the intestinal health and immune function of laying hens by positively influencing the intestinal characteristics, gut microbiota, cecal short-chain fatty acids, and immune parameters.

A convergent approach to side-chain homologated derivatives of 1α,25-dihydroxyergocalciferol

As part of our program on search for vitamin D analogs with selective biological properties, such as low or negligible calcemic action, we describe here an efficient and versatile synthetic approach to derivatives of 1α,25-dihydroxyvitamin D₂ with homologated side-chains and substitution at C24 for biological evaluation.

Ring-A-seco analogs of 1α,25-dihydroxy-19-norvitamin D3

The steroid hormone 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3] is the most active metabolite of vitamin D3 which exerts its control over a multitude of biological processes related to calcium and phosphorus homeostasis, cell proliferation and differentiation, and immune regulation. Unfortunately, the therapeutic application of 1α,25-(OH)2D3 is limited by induction of hypercalcemia. The need for vitamin D compounds with selective biological profiles has stimulated the synthesis of more than three thousand analogs of 1α,25-(OH)2D3. Most of these compounds have structural modifications in the side chain and A-ring; there is also an increasing number of modifications in the CD-rings and limited number in the triene system (seco-B ring). Herein, we report the synthesis and biological evaluation of seco-A-19-nor analogs of 1α,25-dihydroxyvitamin D3, developed to study the role of ring A in the biological activity of 1α,25-(OH)2D3. Interestingly, compounds 2 and 4 show substantial ability to bind the vitamin D receptor and the former is also characterized by selective intestinal calcium transport activity. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

1-desoxy analog of 2MD: synthesis and biological activity of (20S)-25-hydroxy-2-methylene-19-norvitamin D3

During our ongoing structure-activity studies in the vitamin D area, we obtained (20S)-1alpha,25-dihydroxy-2-methylene-19-norvitamin D3 (5). This analog, designated 2MD, is characterized by a significantly enhanced calcemic activity and is currently evaluated as a potential drug for osteoporosis. Therefore, it was of interest to synthesize also its 1-desoxy analog and to evaluate its biological action. These studies were aimed at solving an intriguing problem: can such a vitamin also be hydroxylated in vivo at the allylic C-1 position despite lack of the exomethylene moiety at C-10? The Wittig-Horner coupling of the known protected (20S)-25-hydroxy Grundmann ketone 17 and the phosphine oxides 16 and 33, differing in their hydroxyls protection, provided the target 1-desoxy-2MD (6) after removal of the silyl protecting groups. Two synthetic paths have been elaborated leading to the desired A-ring synthons and starting from commercially available compounds: 1,4-cyclohexanedione monoethylene acetal (7) and (-)-quinic acid (19). The biological activity in vitro of the synthesized 1-desoxy-2MD (6) was evaluated and this analog was found to have an affinity for the vitamin D receptor (VDR) similar as its parent compound 2MD (5) while being much less active in the transcriptional assay. The results of the biological tests in vivo are also discussed.

Degradation chemistry of a Vitamin D analogue (ecalcidene) investigated by HPLC–MS, HPLC–NMR and chemical derivatization

Ecalcidene (1-[(1alpha,3beta,5Z,7E,20S)-1,3-dihydroxy-24-oxo-9,10-secochola-5,7,10(19)-trien-24-yl]-piperidine) is a new 1-hydroxyvitamin D analogue. In this report, the thermal degradation, acid induced degradation and iodine induced degradation of ecalcidene were investigated using HPLC-MS, HPLC-NMR and chemical derivatization. In solution ecalcidene was thermally and reversibly transformed to a pre-Vitamin D type isomer 1 which subsequently produced the dehydrated pyrocalciferol and isopyrocalciferol type isomers 2 and 3 by cyclization and dehydration at elevated temperatures. Acidic conditions resulted in the formation of a novel C9-hydroxylated isomer 4 of ecalcidene, possibly via a tachysterol type intermediate, followed by the acid facilitated nucleophilic addition of water. In the presence of iodine, cis/trans isomerization of both ecalcidene and its pre-Vitamin D type isomer 1 occurred. The results may shed light on the stability and metabolism of ecalcidene, provide useful information for its potential pharmaceutical development, and enrich the knowledge of Vitamin D chemistry.

Synthesis and biological activity of 22-iodo- and (E)-20(22)-dehydro analogues of 1alpha,25-dihydroxyvitamin D3

Construction of 25-hydroxy-steroidal side chain substituted with iodine at C-22 was elaborated on a model PTAD-protected steroidal 5,7-diene and applied to a synthesis of (22R)- and (22S)-22-iodo-1alpha,25-dihydroxyvitamin D3. Configuration at C-22 in the iodinated vitamins, obtained by nucleophilic substitution of the corresponding 22S-tosylates with sodium iodide, was determined by comparison of their iodine-displacement processes and cyclizations leading to isomeric five-membered (22,25)-epoxy-1alpha-hydroxyvitamin D3 compounds. Also, 20(22)-dehydrosteroids have been obtained and their structures established by 1H NMR spectroscopy. When compared to the natural hormone, (E)-20(22)-dehydro-1alpha,25-dihydroxyvitamin D3 was found 4 times less potent in binding to the porcine intestinal vitamin D receptor (VDR) and 2 times less effective in differentiation of HL-60 cells. 22-Iodinated vitamin D analogues showed somewhat lower in vitro activity, whereas (22,25)-epoxy analogues were inactive. Interestingly, it was established that (22S)-22-iodo-1alpha,25-dihydroxyvitamin D3 was 3 times more potent than its (22R)-isomer in binding to VDR and four times more effective in HL-60 cell differentiation assay. The restricted mobility of the side chain of both 22-iodinated vitamin D compounds was analyzed by a systematic conformational search indicating different spatial regions occupied by their 25-oxygen atoms. Preliminary data on the in vivo calcemic activity of the synthesized vitamin D analogues indicate that (E)-20(22)-dehydro-1alpha,25-dihydroxyvitamin D3 and 22-iodo-1alpha,25-dihydroxyvitamin D3 isomers were ca. ten times less potent than the natural hormone 1alpha,25-(OH)2D3 both in intestinal calcium transport and bone calcium mobilization.

Synthesis and photoisomerization of provitamin D analog with 11β,19-oxide bridge

Triol diester 1 was converted into the B-ring 5,7-diene 6 representing the first example of the provitamin D analog where the 10β angular methyl group is connected to ring C by a C11/C19 ether linkage. Ultraviolet light irradiation of 6 resulted in the formation of stereoisomeric 9β, 10α-compound 8a. The structure of the photoproduct was established by analysis of vicinal 1H–1H coupling constants and by molecular mechanics. Keywords: 11β, 19-oxido steroids, lumisterol analog, 5,7-androstadienes, electrocyclic reactions, photochemistry.

Synthesis of 25-hydroxy-[26,27-3H]vitamin D2, 1,25-dihydroxy-[26,27-3H]vitamin D2 and their (24R)-epimers

Synthesis of a C-24-epimeric mixture of 25-hydroxy-[26,27-3H]vitamin D2 and a C-24-epimeric mixture of 1,25-dihydroxy-[26,27-3H]vitamin D2 by the Grignard reaction of the corresponding 25-keto-27-nor-vitamin D2 and 1 alpha-acetoxy-25-keto-27-nor-vitamin D3 with tritiated methyl magnesium bromide is described. Separation of epimers by high-performance liquid chromatography afforded pure radiolabeled vitamins of high specific activity (80 Ci/mmol). The identities and radiochemical purities of 25-hydroxy-[26,27-3H[vitamin D2 and 1,25-dihydroxy-[26,27-3H]vitamin D2 D2 were established by cochromatography with synthetic 25-hydroxyvitamin D2 or 1,25-dihydroxyvitamin D2. Biological activity of 25-hydroxy-[26,27-3H]vitamin D2 was demonstrated by its binding to the rat plasma binding protein for vitamin D compounds, and by its in vitro conversion to 1,25-dihydroxy-[26,27-3H]vitamin D2 by kidney homogenate prepared from vitamin D-deficient chickens. The biological activity of 1,25-dihydroxy-[26,27-3H]vitamin D2 was demonstrated by its binding to the chick intestinal receptor for 1,25-dihydroxyvitamin D3.

Methylcholanthrene: a possible pseudosubstrate for adrenocortical 17 alpha-hydroxylase and aryl hydrocarbon hydroxylase

In cultured bovine adrenocortical cells, loss of 17 alpha-hydroxylase activity was observed after incubation with 3-methylcholanthrene (3-MC). The suppression of 17 alpha-hydroxylase by 3-MC was rapid (50% loss of activity in 10 hr at 1 microM 3-MC), did not exhibit a lag period, and was not affected by cycloheximide. Direct effects of 3-MC on 17 alpha-hydroxylase were observed only at high concentrations, but the concentration for 50% loss of activity was 0.3 microM when 3-MC was added for 24 hr prior to assay of 17 alpha-hydroxylase. High concentrations (to 40 microM) of substrate (progesterone), did not affect the loss of activity due to 3-MC. Loss of 17 alpha-hydroxylase activity was specific; 11 beta-hydroxylase was unaffected and cell growth was unaltered. However, 22-amino-23,24-bisnorchol-5-en-3 beta-ol, an inhibitor of 17 alpha-hydroxylase, partially prevented the loss of 17 alpha-hydroxylase at 1-30 nM. 3-MC is thought to induce cytochrome P-450s via a receptor with high affinity for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD was without effect on 17 alpha-hydroxylase over the range of 10 nM to 10 microM. Benz[a]anthracene, 7,12-dimethylbenz[a]anthracene, benzo[a]pyrene, chrysene, and methylphenanthrenes suppressed 17 alpha-hydroxylase at high concentrations (10-50 microM for 50% loss of activity). Some steroids that lack a substituent at position 17 also caused loss of 17 alpha-hydroxylase. Like 17 alpha-hydroxylase, bovine adreno-cortical cell AHH was found to be suppressed by exposure to 3-MC. Compounds that caused loss of 17 alpha-hydroxylase caused loss of AHH, with a similar order of potency and at similar concentrations. Suppression of AHH by 3-MC did not require protein synthesis and was prevented by an inhibitor of enzymatic activity, alpha-naphthoflavone. This implies a degree of similarity of the cytochrome P-450s for 17 alpha-hydroxylase and adrenal AHH, but the activities were shown to be likely due to different enzymes. The suppression of 17 alpha-hydroxylase and AHH by 3-MC appears not to occur by a receptor-mediated mechanism but to be similar to the suppression of 11 beta-hydroxylase and 21-hydroxylase by steroid pseudosubstrates previously observed.

The respiration and calcium content of heart mitochondria from rats with vitamin D-induced cardionecrosis

Mitochondria were isolated from the heart and skeletal muscle of rats treated with three consecutive daily doses of 100 000 i.u. of calciol (cholecalciferol; 'vitamin D3'). On the fourth day after the last dose, cardiac necrosis developed. At that time mitochondria isolated from heart displayed a 10-fold higher Ca2+ content and a 6-fold lower respiratory rate with pyruvate-plus-malate as substrate as well as with other NAD-dependent substrates. No decrease in respiratory rate with succinate as substrate was observed. EDTA (5 mM) added to the medium during the isolation procedure restored both the high respiratory rate with pyruvate + malate and the low Ca2+ content of the heart mitochondria. The addition of 1 mM-CaCl2 to the medium in which a healthy (control) rat heart had been homogenized caused the same impairment of the mitochondria as did calciol treatment of the animals. No changes of mitochondria isolated from skeletal muscle were observed in rats treated with calciol. It is concluded that the heart mitochondria in vivo fail to accumulate Ca2+ from the cardiac cell overloaded with Ca2+ as the consequence of calciol treatment. Mitochondrial Ca2+ accumulation occurs during the isolation procedure unless an appropriate amount of chelating agent is added to the homogenization medium. The implication of these findings for the biochemical sequence of events in the calciol-induced cardiac necrosis is discussed.

Efficient photochemical formation of 1 alpha-hydroxyprevitamin D3

Control of the band width of the irradiating light between 280 and 310 nm and of the temperature of the reaction permits formation of 1 alpha-hydroxyprevitamin D3 in yields of over 80%, at 40-60% conversion of the 1 alpha-hydroxyprovitamin D3. The procedures developed permit doubling the photochemical yield of the 1 alpha-hydroxyvitamin D3 compounds which are the major circulatory forms of vitamin D3.

Concentration of calcium, phosphorus, and 1,25-dihydroxyvitamin D in plasma of dairy cows during the lactation cycle

Concentrations of calcium, phosphorus, and 1,25-dihydroxyvitamin D in plasma of four young, four nonparetic aged, and four paretic aged cows were measured during the lactation cycle. Concentration of 1,25-dihydroxyvitamin D in plasma was elevated significantly in paretic aged cows as compared to nonparetic aged and young cows from the day of calving to 3 days postcalving. In paretic aged cows, severe hypocalcemia and hypophosphatemia developed on the day of calving, whereas hypocalcemia and hypophosphatemia were only transient in nonparetic aged and young cows at this time. Changes were only minor in concentration of 1,25-dihydroxyvitamin D in plasma from 7 days postcalving to 7 days precalving in all cows.

Characterization of a receptor-like protein for 1,25-dihydroxyvitamin D3 in rat skin

Isolated rat epidermis possesses a cytosolic 3.5 S receptor-like protein for 1,25-dihydroxyvitamin D3. This 3.5S binder has a high affinity (Kd = 1.4 X 10(-10) M) for 1,25-dihydroxyvitamin D3 and is present in low concentrations (31 fmol of binding sites per mg of cytosol protein). Analog competition for receptor binding revealed the following potency order: 1,25-dihydroxyvitamin D3 > 25-hydroxyvitamin D3 > 1 alpha-hydroxyvitamin D3 > 24 (R),25-dihydroxyvitamin D3 > vitamin D3. The receptor has a molecular weight of 60,000, has affinity for DNA-cellulose, and aggregates in the presence of low potassium concentrations. The 1,25-dihydroxyvitamin D3 binder is stabilized by sodium molybdate (10 mM). Addition of phenylmethylsulfonyl fluoride (3 mM) was found to yield more reproducible receptor preparations. The presence of a 1,25-dihydroxyvitamin D3 binding macromolecule with properties similar to those of the bone and intestinal receptor suggests that skin is an additional target organ for this hormone.

Metabolites of 1 alpha, 25-dihydroxyvitamin D3 in rat bile

Metabolites of 1 alpha, 25-dihydroxy[3 alpha-3H]vitamin D3 in rat bile were studied. The water-soluble metabolites (77-91% of the total bile radioactivity) are predominantly acids (retained by DEAE-Sephadex chromatography) that become chloroform soluble after methylation with diazomethane. Calcitroic acid was isolated from this fraction (after conversion to the methyl ester) and unambiguously identified by chromatographic and mass spectrometric studies. The chloroform phase of extracted bile contains small amounts (1.1-8.1% of the metabolites in bile, dependent on dose given) of unchanged 1 alpha, 25-dihydroxyvitamin D3 and no 1 alpha, 24(R),25-trihydroxyvitamin D3. In addition, the chloroform phase contained a mixture of 24-dehydro- and 25-dehydro-1 alpha-hydroxyvitamin D3 and calcitroic acidmethyl ester. The latter compound was shown to be an artifact resulting from the use of methanol as part of the advent mixture for the initial bile extractions.